1,720,955 research outputs found
Hydrothermally-reset magmatic spinels in retrograde serpentinites : formation of ferritchromit rims and chlorite aureoles
No full textSerpentinized harzburgites from southern Tuscany (Italy) host different kinds of spinels: (a) relic, magmatic Al-spinels, (b) hydrothermally altered spinels, occurring as "ferritchromit" rims, (c) syn- and post-serpentinization magnetites. The composition of relic Al-spinels suggests 5-15% partial melting of a fertile, spinel lherzolite. After the main serpentinization, Al-spinels are progressively replaced by ferritchromit rims by a dissolution-recrystallization process. Transmission electron microscopic investigation shows that ferritchromit actually consists of a complex, nanometric association of Cr-magnetite (Mg0.03 Fe0.972+ Al0.11 Cr0.89 Fe3+ 1.00 O4), chlorite and lizardite, with (001)chl/liz always parallel to (111)Cr-mag. Mg and Al, released during the Al-spinel → ferritchromit replacement, interact with mesh-textured serpentine, giving rise to chloritic aureoles (i.e., randomly intergrown chlorite, lizardite and "septechlorite") that overgrow and postdate mesh textures. © Springer-Verlag 2005
Oriented, not-topotactic olivine-serpentine replacement in mesh-textured serpentinized peridotites
No full textPartially serpentinized harzburgites from Southern Tuscany, Italy, show serpentine replacing the peridotitic minerals, as
rims around olivine and thin lamellae parallel to pyroxene cleavage. Exempt from post-serpentinization tectonometamorphic overprints, these mesh-textured serpentinites offer a favourable setting for the study of seafloor serpentinization.
Studied by HRTEM and AEM, the olivine serpentine replacement reveals a complex sequence of reaction steps. Initially,
olivine dissolves forming a silicon-enriched amorphous domain, where early serpentine nuclei are formed. These nuclei recrystallize producing oriented columnar lizardite. The lizardite in the rim shows silicon excess, due to intermixed amorphous or talclike layers. No chrysotile fiber occurs at the reaction front. Although the olivine-to-lizardite reaction is clearly not-topotactic,
recrystallization of early formed serpentine leads to large lizardite sectors, oriented with (001) almost parallel to the reaction front.
As the olivine-to-lizardite reaction is estimated to occur in the upper 300-500°C range, lizardite has to be considered as the
high-temperature serpentine phase in retrograde serpentinites
Exsolution and hydration of pyroxenes from partially-serpentinized harzburgites
No full textOrtho- and clinopyroxenes within partially-hydrated harzburgites from Elba and Val di Cecina (Italy) show lamellar exsolution textures and variable replacement by biopyriboles, talc-chlorite-serpentine mixed layers and serpentine. Chemical and geothermometric data suggest that the pyroxenes crystallized at 1240-1051°C, followed by subsolidus exsolution at slightly lower T (1145-1025°C for clinopyroxene lamellae + orthopyroxene matrix pairs and a 1033-982°C range for orthopyroxene lamellae + clinopyroxene matrix pairs). Investigation by transmission e lectron microscopy of exsolved enstatite and augite reveals a multistage hydration process. The first stage (highest T, probably in the amphibole stability field) leads to the formation of biopyribole lamellae within exsolved augite, leaving the enstatite matrix unaffected. The second stage (∼500-300°C) corresponds to the topotactic replacement of enstatite by layer silicates (talc + chlorite + serpentine, with (001)layer silicates parallel to (100)enstatite). Enstatite is also replaced by randomly oriented, poorly crystalline serpentine. The last hydration stage (<300°C) corresponds to the disappearence of augite and recrystallization of serpentine, leading to completely hydrated bastites with random lizardite lamellae, polygonal serpentine and minor chrysotile. © 2005 The Mineralogical Society
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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